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1© 2018 The MathWorks, Inc.
IEEE 802.11ax
Waveform Generation and Link-level Simulation in
MATLAB with WLAN System Toolbox
Houman Zarrinkoub, PhD.
Product Manager
Communications, LTE and WLAN System Toolboxes
[email protected]
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What is 802.11ax?
▪ IEEE 802.11ax is the latest member of the Wi-Fi standards
▪ Evolution of the popular 802.11ac
▪ HE = High Efficiency
▪ Goals:
– More effectively use 2.4 and 5 GHz bands
– Increase average throughput 4x per user in high-density
scenarios
– Scenarios: corporate offices, stadiums, outdoor hotspots,
dense residential complexes
– Improve outdoor performance
– Improve power efficiency
▪ Backwards compatibility with 11a/b/g/n/ac
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Key Features of 802.11ax
▪ Modulation order up to 1024-QAM
▪ 8x8 Access-Point MIMO
▪ Downlink OFDMA & MU-MIMO
▪ Uplink OFDMA & MU-MIMO
▪ 4x longer Symbol Duration
▪ Extended range preamble
▪ Channel bonding 20MHz 40MHz
TimeSubcarriers
78.125kHz
spacing
1 symbol = 12.8ms
AP
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Enabling technologies:
OFDMA and MU-MIMO
▪ SU-MIMO - all subcarriers (full-band) are
used by one user
▪ MU-MIMO - all subcarriers (full-band) are
used by multiple users
▪ OFDMA - subsets of subcarriers are used
by individual users
▪ MU-MIMO & OFDMA - a subset of
subcarriers are used by multiple users
TimeSubcarriers
TimeSubcarriers
TimeSubcarriers
TimeSubcarriers
User 1
User 2
User 3
User 4
Space
Space
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Rationale: More efficiency
▪ WLAN MAC efficiency drops with increasing number of stations
(users)
▪ Overhead (preamble, MAC headers, …) may consume more time
that
payload data
▪ 802.11n – introduced Aggregation
– Combines short packets in time
▪ 802.11ac – introduced MU-MIMO
– Combines multiple users in space
▪ 802.11ax - introduced OFDMA
– Combines multiple users in frequency dimension
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802.11ax in WLAN System Toolbox
▪ Based on IEEE P802.11ax/D1.1
End-to-End SimulationsSignal Generation
Single User
MU-MIMO & OFDMA
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Waveform Generation Example in MATLAB
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Generating 802.11ax PPDU Formats
cfg = heSUConfig;
cfg = heSUConfig;
cfg.ExtendedRange = true;
cfg = heMUConfig(allocation);
cfg = heTriggerBasedConfig();
tx = heWaveformGenerator(psdu,cfg);
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Resource Units in 802.11ax
▪ OFDMA in 11ax is facilitated by
resource units (RUs)
▪ An RU is a group of 26, 52, 106, 242,
484, 996 or 1992 subcarriers
▪ ≤ 8 users can share an RU (MU-MIMO)
▪ A user can only be assigned to one RU
▪ The number, size, and location of RUs
is defined by an allocation index
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HE-MU Format: OFDMA and MU-MIMO Allocations
▪ An allocation index is required when
creating an HE-MU configuration
▪ For each 20MHz sub-band an allocation index
specifies:
– The number, size and location of RUs
– How many users are assigned to each RU
– Which HE-SIG-B content channel users are
signaled on, for RUs >242-tones
▪ You can easily visualize user allocations
>> plotAllocation(cfg);
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OFDMA and MU-MIMO Allocation in WLAN System Toolbox
▪ Use allocation index to define an 802.11ax configuration
allocationIndex = 136;
cfg = heMUConfig(allocationIndex);
ruInfo(cfg)
ans =
struct with fields:
NumUsers: 4
NumRUs: 3
RUIndices: [1 5 2]
RUSizes: [106 26 106]
NumUsersPerRU: [2 1 1]
NumSpaceTimeStreamsPerRU: [2 1 1]
PowerBoostFactorPerRU: [1 1 1]
Total number of users in
this allocation
Number of resource units
(RUs) in this allocation
136 specifies 3 RUs,
2x106-tone and 1x26 tone
The size and index of
each RU in the allocation
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Configuring Users and RUs
▪ The hierarchy within heMUConfig allows RUs to be
configured:
cfg = heMUConfig(97);
% Configure RU 1 and the user
cfg.RU{1}.User{1}.APEPLength = 1500;
cfg.RU{1}.User{1}.MCS = 2;
cfg.RU{1}.User{1}.NumSpaceTimeStreams = 4;
cfg.RU{1}.User{1}.ChannelCoding = 'LDPC';
cfg.RU{1}.SpatialMapping = 'Direct';
% Configure RU 2, user 1
cfg.RU{2}.User{1}.APEPLength = 1000;
cfg.RU{2}.User{1}.MCS = 3;
cfg.RU{2}.User{1}.NumSpaceTimeStreams = 2;
cfg.RU{2}.User{1}.ChannelCoding = ‘BCC';
% Configure RU 2, user 2
cfg.RU{2}.User{2}.APEPLength = 2000;
cfg.RU{2}.User{2}.MCS = 6;
cfg.RU{2}.User{2}.NumSpaceTimeStreams = 2;
cfg.RU{2}.User{2}.ChannelCoding = ‘LDPC’;
% Configure RU 2 common properties
cfg.RU{2}.SpatialMapping = 'Custom';
cfg.RU{2}.SpatialMappingMatrix = Q;
heMUConfig
ChannelBandwidth
RU
STBC
…
RU{2}
Size
Index
User
SpatialMapping
…
RU{1}
Size
Index
User
SpatialMapping
…
APEPLength
MCS
ChannelCoding
…
User{1}
APEPLength
MCS
ChannelCoding
…
User{1}
APEPLength
MCS
ChannelCoding
…
User{2}
A cell array cfg.RU
contains the
configuration for RUs
A cell array RU{x}.User
contains the configuration for
users within a RU x
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Full-band MU-MIMO Allocations
▪ A full-band MU-MIMO allocation is specified with index
192-223
cfg = heMUConfig(210);
ruInfo(cfg)
ans =
struct with fields:
NumUsers: 3
NumRUs: 1
RUIndices: 1
RUSizes: 996
NumUsersPerRU: 3
NumSpaceTimeStreamsPerRU: 3
PowerBoostFactorPerRU: 1
210 specifies 3 users,
full band 80 MHz
Allocation Index 20 MHz Subchannel Resource Unit
Assignment192-199 (191 + NumUsers ) Full band 20 MHz (1-8
users)
200-207 (199 + NumUsers)Full band 40 MHz (1-8 users), or
448-tone RU with 1-8 users signaled in the corresponding
HE-SIG-B content channel
208-215 (207 + NumUsers)Full band 80 MHz (1-8 users), or
996-tone RU with 1-8 users signaled in the corresponding
HE-SIG-B content channel216-223 (215 + NumUsers ) Full band 160 MHz
(1-8 users)
3 users
All users on
single RU
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OFDMA and MU-MIMO Allocations greater than 20 MHz
▪ An allocation index is required for each 20 MHz subchannel
cfg = heMUConfig([192 192 192 193]);
ruInfo(cfg)
ans =
struct with fields:
NumUsers: 5
NumRUs: 4
RUIndices: [1 2 3 4]
RUSizes: [242 242 242 242]
NumUsersPerRU: [1 1 1 2]
NumSpaceTimeStreamsPerRU: [1 1 1 2]
PowerBoostFactorPerRU: [1 1 1 1]
Four allocation indices defines
an 80 MHz allocation. Each
element specifies the allocation
for a 20MHz subchannel
192 specifies 1 user in
a 242-tone RU193 specifies 2 users
in a 242-tone RU
The 4th RU contains 2 users,
as the allocation index is 193.
The total number of users
is 1+1+1+2 = 5
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WLAN Examples
802.11ax Parameterization for Waveform Generation and
Simulation
Generation of different types of IEEE 802.11ax high
efficiency (HE) formats.
802.11ax OFDMA and Multi-User MIMO Throughput Simulation
Throughput of OFDMA, MU-MIMO, and a combination of
OFDMA and MU-MIMO over TGax indoor channel.
802.11ax Packet Error Rate Simulation for Single User Format
Packet error rate of an 802.11ax single user format link.
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For which aspects of 802.11ax do you want more support?
▪ HE-MU uplink transmission with a single 106-tone RU
▪ Demodulation and decoding of HE trigger-based format
transmissions
▪ 80+80 channel bandwidth
▪ Outdoor TGax channel model
▪ Code generation support
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Summary
▪ Support of single-user, MU-MIMO and OFDMA
– Waveform generation
– End-to-end simulation
▪ Open environment
– MATLAB source code included
– Link to test and measurement instruments, RF, SDRs
▪ Easy configuration and visualization
– Allocation index
– Resource visualization
